1. Technical Field
The present invention relates to a seal used as a shaft seal part in a rotary apparatus for treating a liquid. More particularly, the present invention relates to a mechanical seal suitably used as a shaft seal in a rotary apparatus used in the chemical industry which handles a highly corrosive liquid liable to be readily solidified, particularly a rubber-nature fluid such as latex or the like which can be solidified by shear friction, a plastic fluid which can be copolymerized and solidified by sliding frictional heat, a petroleum fluid such as highly viscous heavy oil or the like, a black liquid used in the pulp industry, muddy water containing a great amount of slurry, or the like.
2. Prior Art
There are known the following mechanical seals as examples of a shaft seal in a pump for delivering a rubber-nature fluid such as latex or the like.
The mechanical seal shown in FIG. 5 is disposed between the outer peripheral surface of a rotary shaft 1, and the inner peripheral surface of a stationary casing 2. An impeller 3 is fitted on the peripheral surface of that part of the rotary shaft 1 at the pump chamber side. A rotary seal ring 4 is disposed between a shaft-seal-side end surface 3a of the impeller 3 and a stepped portion 1a of the rotary shaft 1 which is opposite to the shaft-seal-side end surface 3a. The rotary seal ring 4 is engaged with a knock pin 5 projecting from the end surface 3a of the impeller 3, and is secured to the outer peripheral surface of the rotary shaft 1 with the gap between the end surface 3a and the stepped portion 1a sealed through an O-ring 6. Thus, the rotary seal ring 4 is rotated integrally with the rotary shaft 1.
A retainer 8 is attached to the inner peripheral surface of the casing 2 by a bolt 7. An adapter ring 10 is attached to the retainer 8. The gap between the adapter ring 10 and the inner peripheral surface of the casing 2 is sealed by an O-ring 9. Through a bellows 11 formed from metal, a seal ring retainer 12 is supported by the adapter ring 10. A stationary seal ring 13 having a flat sealing end surface 13a is secured to the seal ring retainer 12. The rotary seal ring 4 has a sharp blade-like sealing end portion 4a, which slides on the sealing end surface 13a.
Secured to the retainer 8 is a buffle ring 14 the tip of which reaches in the vicinity of the inner end of the stationary seal ring 13. At the outer periphery of the buffle ring 14, a mono-coil spring 15 is interposed between the retainer 8 and the seal ring retainer 12, to bias and move the stationary seal ring 13 toward the rotary seal ring 4. Thus, the flat sealing end surface 13a is resiliently pressed against the sealing end portion 4a of the rotary seal ring 4.
The mechanical seal shown in FIG. 6 is of the type where no bellows is used. Likewise in the mechanical seal in FIG. 6, the rotary seal ring 4 is secured to the outer periphery of the rotary shaft 1. On the other hand, the stationary seal ring 13 is secured to the tip of a seal ring retainer 17 disposed at the inner peripheral surface of the casing 2 through an O-ring 16. The stationary seal ring 13 is moved toward the rotary seal ring 4 by the spring load of a plurality of circumferentially disposed multi-coil springs 19 which are held by a spring retainer 18 formed integrally with the casing 2. The blade-like sealing end portion 13a formed at the stationary seal ring 13 is resiliently pressed to the flat sealing end surface 4a of the rotary seal ring 4.
The mechanical seal shown in FIG. 7 is of the type that no bellows is used likewise as in the mechanical seal shown in FIG. 6. The rotary shaft 1 has a small-diameter part 1b at the air side and a large-diameter part 1c at the side of a fluid to be sealed. The rotary seal ring 4 is fitted, in a liquid-tight manner, on the outer periphery of the large-diameter part 1c through an O-ring 20. On the other hand, the stationary seal ring 13 is rotatably fitted on the small-diameter meter part 1b of the rotary shaft 1 and secured to the inner peripheral surface of the casing 2. The rotary seal ring 4 is moved toward the stationary seal ring 13 by the spring load of a plurality of circumferentially disposed multi-coil springs 19 which are held by a spring retainer 21 secured to the outer periphery of the large-diameter part 1c of the rotary shaft 1. The flat sealing end surface 4a of the rotary seal ring 4 is resiliently pressed to the blade-like sealing end portion 13a of the stationary seal ring 13.
In any of the conventional mechanical seals shown in FIGS. 5 to 7, the blade-like sealing end portion 4a or 13a is asymmetrical in configuration in that, as shown in FIG. 8, the outer peripheral surface 4al or 13al of the blade-like sealing end portion 4a or 13a is parallel with the axis of the rotary shaft 1 while the inner peripheral surface 4a2 or 13a2 of the blade-like sealing end portion 4a or 13a is inclined with respect to the axis of the rotary shaft 1. Also as shown in FIG. 8, the angle .theta. formed by the outer peripheral surface 4al or 13al with respect to the edge surface 4a3 or 13a3 is set to 90.degree. or less.
In any of the conventional mechanical seals mentioned above, the inner and outer peripheral surfaces of the blade-like sealing end portion 4a or 13a are asymmetrical with respect to the edge surface. This requires a highly advanced machining technique, so that the production cost is expensive. Further, the angle formed by the outer peripheral surface 4al or 13al with respect to the edge surface 4a3 or 13a3 is not greater than 90.degree.. Accordingly, at the time of machining or when the edge surface 4a3 or 13a3 is resiliently pressed to the flat sealing end surface 13a or 4a and the edge surface 4a3 or 13a3 and the sealing end surface 13a or 4a slide on and come in contact with each other while being rotated, the corner part of the edge surface 4a3 or 13a3 is liable to be broken. This makes it difficult to produce a predetermined sealing effect in a stable manner.
In the conventional mechanical seal shown in FIG. 5, the mono-coil spring 15 is combined with the bellows 11 formed from metal. Accordingly, the structure is not only complicated, but also expensive. Further, the mechanical seal becomes lengthened. Moreover, due to the limited spring load of the metal-formed bellows 11, such a mechanical seal is not suitable for use under the condition of great change in resilient pressure.
In any of the conventional mechanical seals shown in FIGS. 6 and 7, no metal-formed bellows is used. Accordingly, such a mechanical seal is simpler in structure than the mechanical seal in FIG. 5. In the mechanical seal in FIG. 6, however, when the O-ring 16 gets clogged with a solidified body, the retainer 17 cannot be smoothly moved. Further, the balance diameter D becomes great as compared with the edge surface diameter. Accordingly, at the time when the pressure varies, particularly when a reverse pressure is generated, a great opening force acts on the sealing end portion 13a and the sealing end surface 4a. Therefore, the sealing performance is lowered or lost, thus involving the likelihood that the fluid will leak. Accordingly, the application of such a mechanical seal is limited. In the mechanical seal shown in FIG. 7, the multi-coil springs 19 are liable to get clogged with dust, dirt, a solidified body or the like, thus preventing the mechanical seal from properly operating. Further, the O-ring 20 is liable to stick.